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� V �Qc @ s� d Z d d l Z d d l Z d d l Z d d l Z d Z d Z d Z d Z d Z d d d � � YZ d e f d � � YZ d d d � � YZ d � Z d e f d � � YZ d e f d � � YZ e d � Z d � Z e d k r� e � n d S( s� CVS locking algorithm. CVS locking strategy ==================== As reverse engineered from the CVS 1.3 sources (file lock.c): - Locking is done on a per repository basis (but a process can hold write locks for multiple directories); all lock files are placed in the repository and have names beginning with "#cvs.". - Before even attempting to lock, a file "#cvs.tfl.<pid>" is created (and removed again), to test that we can write the repository. [The algorithm can still be fooled (1) if the repository's mode is changed while attempting to lock; (2) if this file exists and is writable but the directory is not.] - While creating the actual read/write lock files (which may exist for a long time), a "meta-lock" is held. The meta-lock is a directory named "#cvs.lock" in the repository. The meta-lock is also held while a write lock is held. - To set a read lock: - acquire the meta-lock - create the file "#cvs.rfl.<pid>" - release the meta-lock - To set a write lock: - acquire the meta-lock - check that there are no files called "#cvs.rfl.*" - if there are, release the meta-lock, sleep, try again - create the file "#cvs.wfl.<pid>" - To release a write lock: - remove the file "#cvs.wfl.<pid>" - rmdir the meta-lock - To release a read lock: - remove the file "#cvs.rfl.<pid>" Additional notes ---------------- - A process should read-lock at most one repository at a time. - A process may write-lock as many repositories as it wishes (to avoid deadlocks, I presume it should always lock them top-down in the directory hierarchy). - A process should make sure it removes all its lock files and directories when it crashes. - Limitation: one user id should not be committing files into the same repository at the same time. 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R R R ( R t nR* R# ( ( s* /usr/lib64/python2.7/Demo/pdist/cvslock.pyR< � s ( R R R+ R R< ( ( ( s* /usr/lib64/python2.7/Demo/pdist/cvslock.pyR; � s c C si xb g } xC | D]: } y | j t | d � � Wq t k rI } ~ Pq Xq WPt | j | | � q t S( Ni ( t appendR; R R" R t list( t repositoriesR t lockst rt instance( ( s* /usr/lib64/python2.7/Demo/pdist/cvslock.pyt MultipleWriteLock� s c C s� d d l } | j d r) | j d } n d } d } d } zD d GHt | � } d GH| j � d GHt | � } d GH| j � Wd d g GHd | _ d g GH| r� | j � n d g GH| r� | j � n d g GHd } d g GHd } d g GHXd S( Ni����i R s attempting write lock ...s got it.s attempting read lock ...i i i i i ( t syst argvR R; R R5 t exc_traceback( RG R t rlt wl( ( s* /usr/lib64/python2.7/Demo/pdist/cvslock.pyt test� s8 t __main__( ( ( t __doc__R R0 R! R- R+ R R R R R R R R" R5 R; RF RL R ( ( ( s* /usr/lib64/python2.7/Demo/pdist/cvslock.pyt <module>G s& ? !